1. Field of the Invention
The present invention relates to a breaking detection method for the power supply line of a motor, which is connected to the motor driven by AC current produced by converting from two phase to three or higher phase, a motor control apparatus and electric power steering mechanism using the same and a computer program thereof.
2. Description of the Related Art
Japanese Patent Application No.HEI11-355585, which is proposed by this inventor also, has disclosed a motor control apparatus for controlling a motor driven by AC current produced by converting from two phase to three or higher phase, for example, to three phase.
In such a motor control apparatus, a current flowing through phase u and phase v of a brushless DC motor is detected by a current detector and after amplified with a predetermined gain, that currents are converted to current detection values iu, iv by an A/D converting circuit and the respective current detection values iu, iv are fetched into a d/q converting portion so as to execute d/q conversion (two-phase conversion). Then, by feeding the current values id, iq obtained thereby back to current instruction values, d-axis current instruction value and q-axis current instruction value, deviations ΔId, ΔIq are obtained and supplied to proportional integration control. With these deviations ΔId, ΔIq, absence/presence of a current flowing through each phase (phase u, phase v, phase w) of the brushless DC motor or absence/presence of a breaking in the power supply line is monitored,
In the meantime, the d/q conversion refers to a method in which while orthogonal coordinates are set with the same direction as magnetic flux of a motor rotator as axis d and a direction perpendicular to this axis d as axis q, AC is calculated as DC by copying the vector of AC current flowing through each phase to that orthogonal coordinates.
However, the conventional motor control apparatus described above monitors which of power supply lines (phase u, phase v, phase w) of AC current is broken or whether or not the current value of each of the current detection values iu, iv, iw becomes zero with the current deviations ΔId, ΔIq on the axis d-q, as shown in FIG. 4(A). For example, because the current detection value iu becomes zero if the power supply line of phase u is broken as shown in FIG. 4(B), the breaking in the power supply line of phase u is detected by the current deviations ΔId, ΔIq obtained by this d/q conversion.
Because usually, this current detection value iu deviates to both polarities of positive and negative as sine wave, the current value becomes almost zero when a rotation angle θ, which crosses zero, is located in the interval of α even if the power supply line is not broken (see FIG. 4). Thus, even if the breaking of the power supply line can be detected when the rotation angle θ of the motor is in the interval of β, the breaking cannot be detected when the rotation angle θ is in the interval of α. That is, there has been produced such a problem that depending upon a detection timing, absence/presence of a breaking of the power supply line cannot be monitored with the current deviations ΔId, ΔIq on the axis d-q alone.